British Prime Minister Theresa May says the United Kingdom carried out "limited, selective and effective" air strikes in Syria overnight in an effort to degrade the country's chemical weapons capability.

The United Kingdom concluded that it was "correct and legal" to take action, together with the United States and France, and to add that the United Kingdom will continue to seek a political solution in Syria.

He said there was a clear intelligence case that the Syrian government had been behind the use of chemical weapons in Douma, and that Russia had blocked diplomatic action to contain the government of Bashar Al-Assad.

"We would have preferred an alternative path, but in this case there was none, we can not allow the use of chemical weapons to normalize," May said in a Downing Street statement.

The United Kingdom has tried "all possible diplomatic channels" to contain the Syrian government, but "our efforts have been thwarted in the UN and at the UN," he added.